My mother reacts the same way in Churches and the way she describes it to me fits perfectly: she feels overwhelmed by other people's negative things. She also told me that she could stand being in a church for more than a few minutes if we were in a monastery or something where people would go there with pure thoughts, not to transform it into a daily gossip place that has nothing to do with the religious aspect more than it has to do with them wanting to be seen in a certain way in other people's eyes, ie, as religious/good people & co.
In my case, the same happened when i was little. It was weird, but i've got to say that it never became so unbearable in a church. The feelings of other people were more overwhelming in classrooms at school, or in buses, or anywhere where more agitated were put together in a small place. For me, churches have always been places when the noise form outside diminishes. Where turning to yourself was something normal and when you could think about your stuff, and cry if you feel like it and be honest and think about truth because this is what you are supposed to do and nobody will butt in. And everytime I feel so good and cleaned, i simply become more peaceful, but at the same time I'm not detached from people or anything, quite on the contrary, I am aware of them. The bad stuff doesn't really stick or simply gets filtered. Your own desire to reach a balance and seek spiritual growth is bigger than the feelings of the people around. But it doesn't have to be something extraordinary. Something you really wish for, someone dear you pray for... should be enough to guard you.
Some people found that they "received" other people's stuff because in their mind they did not truly desire to separate from others, they were still "open" about them, yet ungrounded. It happens on a subconscious level, but this somehow indicates that you've had healthy relationships with people, or you simply need more interaction (or more exercise... daily walks, and walks in nature help alleviate theproblem). Another situation... The mind should be "separated" into certain drawers, and some situations require that you only open the drawers containing certain information/desires/ideas/conceptions/visions to apply in a situation. When you go to a Church and you feel like "ah, i'd have some fun, i'd go to a party, i'd do that, i'd do xyz..."(which is normal from time to time ) ) or if you still seek an answer in people/certain people, or if you have always been compelled to go to church because your parents said so, which i don't really agree with truth be told, you should be prepared to feel more "impure" and earthy emotions. Or you could try to find a better place for yourself. Maybe you need to go to another church. Why don't you take a walk and see what suits you better?
I have quite a few in my town, and there is one, not too big, but pretty and the location gives me a very good vibe, and they have this huge old painting that was gifted from Jerusalem. I'm not sure if the feeling comes from it, but all in all, everytime i walk past it to school, if i happen to be in a more "stressed" state I just snap out of it and remember that i should not embrace such a scattered way of being... Quite interestingly, there's also this bigger and beautiful monastery on my grandparents' town, in a forest who's first quarter is in the city. I don't manage to get the same feeling... and i don't manage to balance myself out. It only worked once, when i was with a friend of mine because she had some problems with her mother. Well, I guess you cannot force it: if it doesn't come, it means the answer is, at that time and moment, in another place, or you have somethign else to do, or for the moment your state is... ok enough. For the most part I'd say i alwys feel a difference when going in and out of a Church, and it is the single place where I always perceived the difference as being directed towards a positive line.
These are some things that i think i caught over time. I guess some perceptions will change as i grow up, but for the moment... i felt like sharing them. Not that sure how these thinking processes go in an American society though, here when i am the majority is orthodox and our churches are more "private"/smaller than the catholic ones.I am also the kind of person that will go to other people to find an answer when I become too tired or something really, really not good is happening. I know i could always isolate/close myself from external influences (i guess this was a protective mechanism) and in turn i had a lot of hobbies, and i was always drawing and crafting things, and be very good with animals. With kids i became good in the latter years only), so what i had to learn was to become more open and perceptive... ^^" and, yeah, probably this is why i presented it in this light. Sorry for my english, it still isn't that good...